1. Field of the Invention
The present invention relates generally to structures for supporting ceramic tile as the tile is conveyed through a firing kiln, and more particularly to such a support structure mounted on a kiln car which is adapted to travel along a set of rails running through a kiln.
2. Description of the Prior Art
As practiced in the art, ceramic wall and floor tile may be kiln fired in a number of ways depending upon the tile body and glaze compositions and upon the size of the tile. For example, tile having a size of about 6".times.6" or larger is typically fired by conveying the tile through the kiln on a roller hearth. On the other hand, tile having a size below about 3".times.3" is typically fired by conveying the tiles through the kiln on a full support slab.
For tiles having a size intermediate the two above mentioned ranges, refractory tile setters have typically been employed. U.S. Pat. No. 3,169,295 to Paspy describes one such tile setter which typically holds about 18-24 tiles. The green (unfired) tile is manually loaded into the setters and a number of loaded setters are placed on a deck of a kiln car. Because of the blocklike configuration of these tile setters, several levels of tile setters can be placed, one on top of another, up to about 4 or 5 levels of tile setters.
While this type of tile setter overcame the problem of tile warpage occurring in earlier tile support systems, they suffered from other drawbacks including the requirement for manual loading and unloading of the tile into and out of the tile setters, manual loading and unloading of the setters on and off of the kiln car as well as enclosing the tiles in a box-like structure. U.S. Pat. No. 3,756,581 discloses another tile setter which also has this enclosed structure. The closed box-like structure limits the amount of air flow passing over the tiles and effectively lengthens the tile firing cycle in the kiln. The longer firing cycle translates into higher kiln fuel consumption per unit number of tiles produced.
In response to these defficiencies in the art, U.S. Pat. No. 4,462,798 to Foster discloses a more open support structure for the firing of ware of variable size. This patent utilizes large shelf slabs for supporting the ware so that ware having varied sizes and shapes, including over-sized ware, can be fired. Because of the large and heavy shelf slabs and the overall height of the ware support structure in the Foster patent, the structural members are made of recrystallized silicon carbide, a lightweight refractory material having exceptional strength, but a cost of about ten times that of conventional refractories. The apparatus disclosed in the Foster patent is accordingly very expensive to manufacture. In addition, because of the relatively heavy support blocks in which the silicon carbide posts are anchored, the overall kiln weight is somewhat high. This results in less efficient kiln operation since a greater portion of the heat from the kiln is absorbed by the mass of the kiln car and the support structure rather than the ware being fired.
Thus, it is an object of the present invention to provide a tile firing support structure, adapted to be mounted on a kiln car and having both a low mass and a relatively open structure, which minimizes the degree of contact between the support structure and the surface of the tile while maximizing the amount of free air flow around the tile thereby allowing the tile to be fire over a shorter firing cycle.
It is a further object of the invention to provide a tile firing support structure in which the tile density (i.e., the number of supported tiles per unit volume of space) is adjustable thereby allowing greater compatability with automated tile loading and unloading systems.
It is another important object to minimize the cost of the tile firing support structure by using lower cost refractory pieces which can be formed by punch pressing rather than by the expensive and time consuming casting and machining procedures used to make the prior art tile setters. It is also an object to minimize the cost of the tile firing support structure through judicious use of expensive refractory materials such as recrystallized silicon carbide as well as minimizing kiln fuel consumption per unit number of tiles produced.